The Pentagon held internal talks on declassifying sensitive missile defense technology that it plans to share with Russia as part of the Obama administration’s efforts to assuage Moscow’s opposition to European defenses.

Republicans in both the House and Senate plan to block any technology declassification for missile defense technology in the current defense authorization bill and other legislation. Legislative mark up on the authorization bill begins this week.

Critics say giving Russia classified data would undermine the effectiveness of missile defenses, which have cost taxpayers more than $100 billion since the 1980s.

Vice Adm. James Syring, director of the Pentagon’s Missile Defense Agency (MDA), disclosed during a congressional hearing Wednesday that the Obama administration has asked him about sharing sensitive missile defense data with Russia during talks over the past several years aimed at reaching a missile defense cooperation agreement.